Real-time Transport Protocol (RTP) is used widely for the transmission of real-time or near-real-time data over IP networks. It comes with a companion protocol named Real-time Transport Control Protocol (RTCP), which is used to monitor the transmission, collecting statistics and sending control data in the forward transmission direction or as a feedback from the receiver back to the sender.
RTP normally restricts the amount of feedback by two rules: First there is a certain fraction (recommended to be 5%) of the RTP session bandwidth allocated for RTCP. All receivers share this bandwidth and calculate from this value the time duration, during which they send the feedback. The second rule is that the interval between two feedback transmissions must be at least five seconds (five seconds as the recommended value).
While these rules make RTP stable and usable for large multicast groups, it is not optimized for unicast or small multicast transmissions. In these groups more feedback per user would be beneficial and could be sent. The problem was already identified. In an extended version of the a new RTP protocol, the rule that the interval between two feedback transmissions must be at least five seconds is omitted. Thus the receiver can send much more feedback, depending on the session parameters. The rule that the allocated RTCP session bandwidth must not be exceeded is still valid.
As mentioned above, the fraction of RTP bandwidth for the transmission of control data that is allocated for RTCP is generally fixed to a recommended value of 5%. However a solution is presently standardized to change this fraction to other values. The bit rate can also be set to zero in order to turn RTCP feedback off.